1. Field of the Invention
The present invention relates to a method and base station system for configuring a radio interface between a mobile station and a base station in a time-division multiplex mobile radio system for packet data transmission.
2. Description of the Prior Art
Connection-oriented concepts and concepts based on logic links may be used to transmit data between two communications terminals. In the case of connection-oriented data transmissions, physical resources must be provided between the two communications terminals throughout the entire time for data transmission.
Permanent provision of physical resources is unnecessary for data transmission via logical links. One example of such data transmission is packet data transmission. In this case, a logic link exists between the two communications terminals throughout the entire duration of data transmission, but physical resources are provided only during the actual transmission times for the data packets. This method is based on the fact that the data are transmitted in short data packets, between which relatively long pauses may occur. In the pauses between the data packets, the physical resources are available for other logic links. A logic link results in a saving of physical resources.
The packet data transmission method known from DE 44 02 903 A1 and EP 0 681 406 A1 can be used in particular for communications systems with limited physical resources. For example, in mobile radio systems such as the GSM mobile radio system (Global System for Mobile Communications), the physical resources in the frequency band—[lacuna] [lacuna] number of frequency channels and time slot—are limited and must be used economically.
The GSM mobile radio system is one example of a time-division multiplex mobile radio system in which time slots within a frequency channel can be split between different communications terminals. The radio station at the network end of a mobile radio network is a base station which communicates with mobile stations via a radio interface. Transmission from a mobile station to the base station is called the uplink direction and transmission from the base station to a mobile station is called the downlink direction. A channel, which is reserved for packet data transmission, is formed by at least one time slot per time-division multiplex frame. Furthermore, the channel is defined by the carrier frequency and any frequency jump sequence.
The GSM mobile radio system was originally conceived for voice transmission, and one channel was reserved for continuous information transmission between the mobile station and the base station. However, for packet data transmission, a common channel is used for packet data transmission for a plurality of mobile stations. In addition to the packet data, signalling information is also transmitted for which a time slot is provided at cyclic intervals within the channel.
The distinction between logic links and physical connections also means that, although a logic link exists for a mobile station, no packet data is transmitted over a certain time interval. However, as long as there is no transmission from the mobile station to the base station, it is impossible for the base station to carry out any measurements relating to the transmission conditions from the mobile station. Previously calculated values lose their validity and must be redefined during renewed allocation of physical channels, or the base station must ensure that the transmission conditions are set in such a manner that reliable transmission is possible in every case. The latter leads, for example, to an excessive, or even maximum, transmission power setting. DE 195 34 156 C1 discloses the determination of the timing advance being suppressed in the absence of specific decision criteria.
As a consequence, the present invention is based on the object of specifying a method at a base station system for improved configuration of a radio interface for packet data transmission.